4-aminodiphenylamine (4-ADPA) is an important precursor in the synthesis of anti-ageing agents and stabilisers in the rubber and polymer industry (Kirk-Othmer, Encyclopedia of Chemical Technology, 4th Edition, 1992, Vol. 3, pp. 424-456; Ullmann's Encyclopedia of Industrial Chemistry, 5th Edition, Vol. A3, 1985, pp. 91-111).
4-ADPA may be produced by various methods. One possible way of producing 4-ADPA is the two-stage reaction of aniline or aniline derivatives with p-nitro-chlorobenzene in the presence of an acid acceptor or a neutralising agent, and optionally in the presence of a catalyst. The production according to this method is described for example in DE-A 3 246 151, DE-A 3 501 698, DE-A 185 663, U.S. Pat. Nos. 4,670,595, 4,187,249, 4,683,332 and 4,187,248. The first stage is generally carried out with copper catalysts, and the second stage with metal components different therefrom, for example nickel (see for example U.S. Pat. No. 5,840,982). Reactions of for example also halogenated nitrobenzenes with amines in the presence of palladium catalysts are described in U.S. Pat. No. 5,576,460 and EP-A 846 676.
A disadvantage of the production method identified above using copper catalysis is the comparatively poor selectivity of the reaction with regards to the formation of the desired diarylamine. The 5-15% of the triarylamine that is normally formed results in an increased distillative expenditure for the purification of the end product, as well as in economic drawbacks due to increased consumption of the valuable component halogenated nitrobenzene, since two equivalents of halogenated nitrobenzene are consumed per one equivalent of triarylamine that is formed. In addition the disposal of the byproduct represents an ecological problem.
It was therefore desirable to provide a process for the production of amino-diphenylamines that starts from anilines and leads, by reaction with corresponding nitrohalogenated benzenes, to nitrodiphenylamines followed by reduction of the intermediate product that is formed in relatively high yield and with reduced formation of the triarylamine product, to the desired aminodiphenylamines.
Venkataraman et al. [Tetrahedron Letters, 2001, 42, 4791-4793] were able to show that the use of a preformed complex of copper dibromide and triphenyl-phosphine produces a novel catalyst that catalyses the addition of aryl halides to secondary aromatic amines with the formation of triarylamine.
The addition of aryl halides to primary amines does not, however, as shown in a comparison example, provide any significant advantages compared to the Cu/Cs catalyst system known from DE 3 246 151 A1.
It was therefore surprising that the use of certain copper-phosphorus complexes in the reaction of nitrohalogenated benzenes with anilines yields only very small amounts of the undesired triarylamine as byproduct. Also surprising was the raised catalytic activity of these complexes with respect to the formation of nitrodiphenylamines.